Dione stretches just 698 miles across, making it Saturn's 15th largest moon. Saturn hosts 62 known moons. Surprisingly, Dione is larger than all of its more diminutive peers combined.

Astronomers believe Dione's outer layers of water ice hide a dense core made of silicate rock. And because the satellite is so cold -- negative 304 degrees Fahrenheit on most days -- its ice layers behave like rock.